Volta Charging, the San Francisco-based company that combines outdoor digital advertising with charging stations to give electric vehicle owners free power, has added another $20 million in a follow-on to its Series C round.

The company’s Series C round is now closed at $100 million. Schneider Electric Ventures, SK Innovation, Energize Ventures and a number of existing partners participated in the follow-on Series C round. Volta Charging also borrowed $44 million from Energy Impact Partners and CION.

Volta, which launched in 2010, partners with businesses and real estate owners to install EV chargers in high-traffic areas such as grocery stores, entertainment venues and shopping centers. Instead of charging EV owners, the power is provided for free. Volta makes money on the outdoor advertising that is a centerpiece of the charger design.

More than 45 million free electric miles have been given to EV drivers to date, the company said.

The company’s first charging stations popped up in Hawaii. Since then, Volta has expanded to San Diego, Los Angeles, San Francisco and Silicon Valley in California as well as Chicago and its suburbs, Phoenix, and Dallas and Houston.

The funds will be used to expand the company’s network of free, advertiser sponsored charging stations. Volta is focused on adding more chargers to cities where it already has a presence as well as moving into new markets.

“As the electric vehicle industry continues to grow, Volta is well-positioned to build out an economically viable charging network needed to facilitate the shift from gas to electric,” Volta CEO and founder said Scott Mercer said in a statement. “We continue to rapidly scale our business to meet the growing demands of drivers, real estate partners and sponsors. This capital injection will accelerate our mission of mainstreaming electric vehicles.”